1. Field of the invention
The present invention relates to an electronic radiography system for imaging radiographic images and a signal relay device.
2. Description Related to the Prior Art
In medical fields, radiography systems, for example, X-ray imaging systems using X-rays are widely used to examine inside human bodies. The X-ray imaging system comprises an X-ray generating apparatus that generates X-rays and an X-ray imaging apparatus for imaging X-ray images generated by the X-rays passed through a subject (patient). The X-ray generating apparatus comprises an X-ray source that applies the X-rays to the subject, a source control device that controls the drive of the X-ray source, and an emission switch that allows emission of the X-rays.
X-ray image detection devices (hereinafter referred to as the electronic X-ray image detection devices) that electronically detect X-ray images have been prevailing as X-ray imaging apparatuses, in place of X-ray image recording devices using X-ray films and X-ray image detection devices using IP plates. In the X-ray imaging system (hereinafter referred to as the electronic X-ray imaging system) using the electronic X-ray image detection device, the electronic X-ray image detection device is connected to a console. The X-ray image detected by the electronic X-ray image detection device is transmitted to the console, and displayed on a display of the console. The electronic X-ray image detection device comprises a sensor panel referred to as a flat panel detector (FPD). The sensor panel has an imaging field in which pixels are arranged in a matrix. Each pixel stores a signal charge in accordance with an amount of incident X-rays. The sensor panel stores signal charge in each pixel at the time of X-ray imaging, and the stored signal charges are read out to a signal processing circuit through switching elements such as TFTs (thin film transistors). The signal processing circuit converts the signal charges into a voltage signal and outputs the voltage signal as an X-ray image signal.
Recently, there has been a growing trend to modify a conventional or existing X-ray imaging system, which uses the X-ray image recording device using the X-ray film or the X-ray image detection device using the IP plate, into the electronic X-ray imaging system. In this modification, the electronic X-ray detection device and the console are replaced while the existing X-ray generating apparatus is used without replacement because the modifications to the entire system results in high introduction cost.
The electronic X-ray image detection device differs from the X-ray image recording device using the X-ray film and the X-ray image detection device using the IP plate in that a reset operation, in which dark charge noise is discharged, needs to be performed at regular time intervals before imaging. When the X-ray imaging is started, a storage operation to store a signal charge, which corresponds to the amount of the incident X-rays, in each pixel is started after the reset operation. Therefore it is necessary to synchronize the timing for starting the storage operation with the timing to start the X-ray emission from the X-ray source. In a case where the existing X-ray generating apparatus is used for the electronic X-ray imaging system, it is necessary to make modifications so as to transmit an emission command signal from the emission switch to each of the source control device and the electronic X-ray image detection device.
In PCT International Publication No. WO 2009/067189 (corresponding to Japanese translation of PCT international application publication No. 2011-502699), a signal relay device (which serves as both connection circuit and control circuit) is used to make minimum modifications to the existing X-ray generating apparatus. The signal relay device is connected to each of the emission switch (operation switch), the source control device (console and X-ray generator), and the electronic X-ray image detection device (DR receiver panel). The signal relay device transmits the emission command signal (exposure signal) from the emission switch to each of the source control device and the electronic X-ray image detection device.
An electronic X-ray imaging system described in the PCT International Publication No. WO 2009/067189 is provided with an automatic exposure control device (hereinafter abbreviated as the AEC device) to control exposure of the X-ray image. The AEC device stops the X-ray emission from the X-ray source when an X-ray dose (cumulative dose) reaches a target amount. In a case where the AEC device is used, it is necessary to input an emission stop signal from the AEC device to the source control device. For this reason, the source control device is provided with an AEC I/F, which receives the emission stop signal from the AEC device, in addition to a switch I/F, to which the emission command signal is inputted. The source control device drives the X-ray source to allow the X-ray emission while the emission command signal is inputted from the switch I/F, but disables the X-ray source to forcefully terminate its X-ray emission upon the input of the emission stop signal from the AEC device through the AEC I/F.
The electronic X-ray image detection device described in U.S. Pat. No. 8,841,620 (corresponding to Japanese Patent Laid-Open Publication No. 2011-174908) comprises an AEC function to measure the X-ray dose with a sensor panel and determine timing to stop the X-ray emission from the X-ray source.
In many cases, the AEC I/F of the source control device allows connecting a predetermined AEC device only. In a case where the AEC function of the electronic X-ray image detection device of the U.S. Pat. No. 8,841,620 is utilized for the X-ray generating apparatus of the PCT International Publication No. WO 2009/067189, it is necessary to modify the AEC I/F of the source control device in accordance with the specifications of the AEC function of the electronic X-ray image detection device. It is also necessary to modify a control sequence for the source control device to stop the X-ray emission. Even if the source control device does not have the AEC I/F, it is necessary to modify the source control device to utilize the AEC function of the electronic X-ray image detection device.